RESUMO
OBJECTIVE: Central venous-arterial PCO2 to arterial-central venous O2 content ratio (Pcv-aCO2/Ca-cvO2) is commonly used as a surrogate for respiratory quotient (RQ) and tissue oxygenation. Although Pcv-aCO2/Ca-cvO2 might be associated with hyperlactatemia and outcome, neither the interchangeability with RQ nor the correlation with conclusive variables of anaerobic metabolism has never been demonstrated in septic shock. Our goal was to compare Pcv-aCO2/Ca-cvO2 and RQ in patients with septic shock. DESIGN: Prospective, observational study. SETTING: Two adult ICUs. PATIENTS: Forty-seven patients with septic shock on mechanical ventilation with stable respiratory settings and vasopressor dose after initial resuscitation. INTERVENTIONS: None. MAIN VARIABLES OF INTEREST: We measured arterial and central venous gases, Hb, and O2Hb. Pcv-aCO2/Ca-cvO2 and the ratio of central venous-arterial CO2 content to arterial-central venous O2 content (Ccv-aCO2/Ca-cvO2) were calculated. RQ was determined by indirect calorimetry. RESULTS: Pcv-aCO2/Ca-cvO2 and Ccv-aCO2/Ca-cvO2 were not correlated with RQ (R2 = 0.01, P = 0.50 and R2 = 0.01, P = 0.58, respectively), showing large bias and wide 95 % limits of agreement with RQ (1.09, -1.10-3.27 and 0.42, -1.53-2.37). A multiple linear regression model showed Hb, and central venous PCO2 and O2Hb, but not RQ, as Pcv-aCO2/Ca-cvO2 determinants (R2 = 0.36, P = 0.0007). CONCLUSIONS: In patients with septic shock, Pcv-aCO2/Ca-cvO2 did not correlate with RQ and was mainly determined by factors that modify the dissociation of CO2 from Hb. Pcv-aCO2/Ca-cvO2 seems to be a poor surrogate for RQ; therefore, its values should be interpreted with caution.
RESUMO
The key objective in the hemodynamic treatment of septic shock is the optimization of tissue perfusion and oxygenation. This is usually achieved by the utilization of fluids, vasopressors, and inotropes. Dobutamine is the inotrope most commonly recommended and used for this purpose. Despite the fact that dobutamine was introduced almost half a century ago in the treatment of septic shock, and there is widespread use of the drug, several aspects of its pharmacodynamics remain poorly understood. In normal subjects, dobutamine increases contractility and lacks a direct effect on vascular tone. This results in augmented cardiac output and blood pressure, with reflex reduction in systemic vascular resistance. In septic shock, some experimental and clinical research suggest beneficial effects on systemic and regional perfusion. Nevertheless, other studies found heterogeneous and unpredictable effects with frequent side effects. In this narrative review, we discuss the pharmacodynamic characteristics of dobutamine and its physiologic actions in different settings, with special reference to septic shock. We discuss studies showing that dobutamine frequently induces tachycardia and vasodilation, without positive actions on contractility. Since untoward effects are often found and therapeutic benefits are occasional, its profile of efficacy and safety seems low. Therefore, we recommend that the use of dobutamine in septic shock should be cautious. Before a final decision about its prescription, efficacy, and tolerance should be evaluated throughout a short period with narrow monitoring of its wanted and side effects.